In a typical turbine engine, also known as a gas turbine or a combustion turbine, an upstream compressor is coupled to a downstream turbine, and a combustion chamber is located in-between. A gas stream enters the turbine engine from the compressor end, and is highly pressurized in the upstream compressor; the compressed gas stream subsequently enters the combustion chamber at a high velocity, fuel is added thereto and ignited to impart additional energy to the gas stream; the energized gas stream subsequently drives the downstream turbine.
In principle, efficiency of a turbine engine varies in direct relation to operating temperature in the combustion chamber. Thus, in order to achieve high efficiency, it is desirable to operate the combustion chamber at a high temperature. Accordingly, the combustion chamber is operated at high temperatures often exceeding 1,200 degrees Centigrade. However, the maximum operating temperature is limited by the thermal strength of various internal components, and in particular, turbine blades located in the downstream turbine. In order to increase the thermal strength thereof, the turbine blades must be made of materials capable of withstanding such high temperatures. In addition, the turbine blades are provided with various cooling arrangements for increasing tolerance towards excessive temperatures, and thereby, prolonging the life of the blades.
Typically, turbine blades include a root portion and a platform at one end and an elongated portion forming a blade that extends outwardly from the platform. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge extending from the platform adjacent to the root section to the tip of the turbine blade. Such turbine blades have a hollow construction and contain an intricate maze of cooling channels forming a cooling arrangement. In a typical turbine blade cooling arrangement, cooling fluid is tapped from the compressor and provided to the cooling channels in the turbine blades. The cooling channels often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature.
Several different cooling arrangements based on a combination of convective, impingement, and external film-based cooling have been proposed in the state of the art. In a typical cooling arrangement for a turbine blade, longitudinal partitions are formed inside a turbine blade, which, together with side walls of the turbine blade, form a supply chamber and, adjacent to the supply chamber, one or more impingement cooling chambers. The cooling fluid flows from the supply chambers into the adjacent impingement cooling chambers, thereby intensely cooling the turbine blade from the inside and enabling the turbine engine to be operated with high efficiency at high combustion temperatures. The cooling fluid exits from the impingement cooling chambers through film-cooling holes in the sidewalls of the turbine blade creating a barrier layer between the outer surface of the turbine blade and the hot gas, which further reduces the thermal load on the turbine blade.
As mentioned earlier, the cooling fluid supplied to the cooling arrangement in a turbine blade is bled from the upstream compressor, and thus, represents additional energy consumption in the turbine engine. Hence, the efficiency of the cooling arrangement is an important consideration in design of turbine engine since the efficiency of the cooling arrangement impacts not only overall operational life of the turbine engine components but also overall efficiency of the turbine engine itself.
The documents U.S. Pat. No. 8,011,888 B1, U.S. Pat. No. 8,061,990 B1, U.S. Pat. No. 7,625,180 B1, U.S. Pat. No. 7,527,475 B1, U.S. Pat. No. 7,985,050 B1, EP 1 953343 A2 disclose a turbine blade according to the preamble of the independent claim.
It is therefore desirable to provide an improved cooling arrangement such that increased cooling efficiency is achieved, that is, an amount of cooling fluid required for desired heat removal is reduced.